CN107852468B

CN107852468B - Radiation image pickup device

Info

Publication number: CN107852468B
Application number: CN201680037385.6A
Authority: CN
Inventors: 饭塚邦彦; 田口滋也; 柏木克久
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2015-06-30
Filing date: 2016-03-10
Publication date: 2019-12-27
Anticipated expiration: 2036-03-10
Also published as: US10165999B2; US20180249976A1; WO2017002403A1; EP3319309A1; CN107852468A; JPWO2017002403A1; JP6416397B2; EP3319309B1; EP3319309A4

Abstract

The purpose is to improve the frame rate and suppress power consumption. A radiation image capturing device (100) is provided with: a plurality of pixels; a capacitor element (1a) that accumulates charges corresponding to the radiation dose (X) of the radiation; and a read control unit (read element control unit 22, reset element control unit 23) for reading an output (output voltage Vout) corresponding to the electric charge from at least one pixel (active pixel 10) which is not initialized for two or more frames.

Description

Radiation image pickup device

Technical Field

The present invention relates to an image pickup apparatus using radiation, particularly X-rays.

Background

Conventionally, development of a radiographic image capturing panel in which sensor elements that output electric charges (electric signals) corresponding to a radiation dose of radiation, particularly X-rays, irradiated on a subject are arranged two-dimensionally has been underway. The sensor element is provided in each of a plurality of pixels arranged in a two-dimensional matrix on a substrate (panel). In this radiographic image capturing panel, the charges are accumulated in a capacitor element provided in each pixel, and an output corresponding to the accumulated charges from each pixel is read and controlled by a Thin Film Transistor (TFT) element.

In particular, in recent years, there has been an increasing demand for reducing the influence of noise generated in a circuit or the like for reading an output corresponding to accumulated charges. In response to this demand, an active pixel type radiographic image capturing panel in which a TFT element as an amplifying element is further provided in a pixel, and the output is amplified and transmitted to the circuit, and an imaging device provided with the panel have been actively developed.

For example, patent document 1 and non-patent document 1 disclose an active pixel sensor including a TFT for AMP (output amplification), a TFT for READ (output READ), and a TFT for RESET (RESET of the active pixel sensor). Here, the reset of the active pixel sensor means that the gate voltage of the TFT for AMP is returned to a set initial potential so that the current between the drain and the source of the TFT for AMP becomes a predetermined value. In addition, as a conventional active pixel sensor, there is a case where the three TFTs and the sensor element are connected as shown in fig. 1. As shown in fig. 2, the conventional active pixel type radiographic imaging panel includes active pixel sensors shown in fig. 1 arranged in a two-dimensional matrix on a substrate, and a Reset signal generation circuit, a Read signal generation circuit, a control circuit, and a current/voltage conversion amplifier. In fig. 2, the number of active pixel sensors is 4 × 4 and 16 in total for convenience of description. The Reset signal generation circuit generates and outputs signals Reset _1 'to Reset _ 4' for resetting the active pixel sensor. The Read signal generation circuit generates and outputs signals Read _1 'to Read _ 4' for reading output currents Iout _1 'to Iout _ 4' from the respective active pixel sensors.

Next, fig. 3 shows an example of a timing chart of an image capturing operation of the image capturing apparatus including the image capturing panel shown in fig. 2. As shown in fig. 3, the image pickup apparatus resets the capacitive elements of all the active pixel sensors every time it takes to read data of one two-dimensional image. Fig. 4 shows another example of a timing chart of an image capturing operation of the image capturing apparatus. As shown in fig. 4, the image pickup apparatus interrupts reading of two-dimensional image data, resets the active pixel sensor, and then reads again. This operation is performed in units of rows of the active pixel sensors, and is performed for all rows of the active pixel sensors within a time required to read data of one two-dimensional image.

Documents of the prior art

Patent document

Patent document 1: U.S. published patent publication "US 2004/0135911A 1 (published 7/15/2004)"

Non-patent document

Non-patent document 1: taghibakhsh, f.; karim, K.S., "Two-train passive Pixel Sensor for High Resolution Large Area Di digital X-ray Imaging," IEEEInternational Electron Devices Me et 2007, pp.1011,1014,10-12, Dec.2007

Disclosure of Invention

Technical problem to be solved by the invention

However, although patent document 1 and non-patent document 1 disclose that the RESET of the active pixel sensor and the output read are performed within a time (read time) during which the output read is performed, a technique of controlling a RESET terminal so as not to perform the RESET within the read time is not disclosed. Therefore, in the imaging device including a plurality of the above-described active pixel sensors, when all the active pixel sensors are reset every reading time, there are the following problems compared to the case where there are active pixel sensors that are not reset: the reading time of the time required for reset becomes long, and the power consumption of the image pickup apparatus increases. Further, even in an imaging apparatus including a conventional active pixel type radiation image capturing panel, since all the active pixel sensors are reset every time it takes to read data of one two-dimensional image, the same problem as described above is present.

The present invention has been made to solve the above-described problems, and an object thereof is to provide a radiographic imaging apparatus that achieves an improvement in frame rate and a reduction in power consumption by shortening the total acquisition time of two-dimensional image data.

Means for solving the problems

In order to solve the above problem, a radiographic imaging device according to one aspect of the present invention is a radiographic imaging device that acquires a two-dimensional image corresponding to a radiation dose of radiation that has been irradiated to a subject, the radiographic imaging device including: a plurality of pixels arranged two-dimensionally; a capacitance element provided in each of the plurality of pixels, and configured to accumulate charges corresponding to the radiation dose per pixel between at least two consecutive frames by incidence of the radiation to the plurality of pixels; and a reading control unit that reads, from at least one pixel of the plurality of pixels, a first output and a second output corresponding to the accumulated electric charges, without initializing the at least one pixel in each of a first frame and a second frame constituting the two frames.

Effects of the invention

According to one aspect of the present invention, by not initializing at least one pixel in each of consecutive first and second frames, it is possible to improve the frame rate and suppress power consumption.

Drawings

Fig. 1 is a circuit diagram showing a conventional active pixel and a main part of an active pixel provided in a radiation image capturing apparatus according to a first embodiment of the present invention.

Fig. 2 is a circuit diagram showing a main part of an imaging device including a conventional active pixel type radiation image capturing panel.

Fig. 3 is a diagram showing an example of a timing chart of an image capturing operation of the image capturing apparatus.

Fig. 4 is a diagram showing another example of a timing chart of an image capturing operation of the image capturing apparatus.

Fig. 5 is a circuit diagram showing a main part of a radiation image capturing apparatus according to a first embodiment of the present invention.

Fig. 6 is a timing chart showing an image capturing operation of the radiation image capturing apparatus.

Fig. 7 is a graph showing a relationship between a dose of radiation incident on an active pixel provided in the radiographic imaging device and an output voltage from the active pixel.

Fig. 8 is a flowchart showing an image capturing process of the radiation image capturing apparatus.

Fig. 9 is a circuit diagram showing a main part of a radiation image capturing apparatus according to a second embodiment of the present invention.

Fig. 10 is a timing chart showing an image capturing operation of the radiation image capturing apparatus.

Fig. 11 is a graph showing a relationship between a dose of radiation incident on an active pixel provided in a radiographic imaging device according to a third embodiment of the present invention and an output voltage from the active pixel.

Fig. 12 is a graph showing a relationship between the radiation dose of the radioactivity and the output voltage by an approximation function.

Detailed Description

[ first embodiment ]

Hereinafter, embodiments of the present invention will be described in detail with reference to fig. 1 and 5 to 8.

< construction of radiographic imaging apparatus >

First, a main configuration of the radiation image capturing apparatus 100 will be described. Fig. 5 is a circuit diagram showing a main part of the radiation image capturing apparatus 100. The radiographic imaging device 100 performs moving image imaging by continuously generating two-dimensional image data corresponding to the radiation dose X of radiation irradiated to an object. As shown in fig. 5, the radiographic imaging device 100 includes: an imaging panel 20, a control unit 21, a reading element control unit (reading control unit) 22, a reset element control unit (reset control unit) 23, a current/voltage conversion amplifier (hereinafter abbreviated as "IV amplifier") 24, and an image data generation unit (output generation unit) 25.

The imaging panel 20 is a flat plate-like base material, and a total of n rows by n columns is arranged in a matrix in a plan view²An active pixel (pixels) 10. The number and arrangement of the active pixels 10 are not particularly limited as long as they are two-dimensionally arranged, but in fig. 2, an arrangement of 4 rows × 4 columns is illustrated for simplicity of the drawing.

The control unit 21 controls the reading device control unit 22, the reset device control unit 23, and the image data generation unit 25, and also performs overall control of the radiographic imaging device 100.

The Read element control unit 22 outputs Read signals Read _1 to Read _4 to the gate electrodes of the Read elements 3 (described later with reference to fig. 1) of each row of the active pixels 10 (each row is constituted by four active pixels 10), thereby controlling the reading of the output currents Iout _1 to Iout _4 by the Read elements 3. The Read signals Read _1 to Read _4 have a High level (High) period for executing reading and a Low level (Low) period for interrupting reading.

The Reset element control unit 23 outputs a Reset signal Reset _ all to the gate electrodes of all the Reset elements 4 (described later with reference to fig. 1) to control initialization of the active pixels 10 by the Reset elements 4. The Reset signal Reset _ all has a High level (High) period for initialization execution and a Low level (Low) period for initialization interruption.

The IV amplifier 24 converts the output currents Iout _1 to Iout _4 output from the reading element 3 into output voltages Vout _1 to Vout _4, and outputs the output voltages to the image data generation unit 25.

Based on the input output voltages Vout _1 to Vout _4, the image data generation section 25 generates data of a two-dimensional image of 4 × 4 resolution proportional to the amount of change Δ X in the radiation dose X of the radiation incident on the active pixels 10. The data processing of the image data generating unit 25 will be described later.

In addition, details of the capacitive element 1a, the reading element 3, the reset element 4, the active pixel 10, and the initialization of the active pixel 10 will be described below.

< construction of active Pixel >

Next, the main structure of the active pixel 10 will be described. Fig. 1 is a circuit diagram showing a main part of an active pixel 10. The active pixel 10 converts a radiation dose X of radiation irradiated to an object into an output current Iout for two-dimensional image data generation and outputs the output current Iout. As shown in fig. 1, the active pixel 10 includes a sensor element 1, an amplifying element 2, a reading element 3, and a reset element 4.

In each of the following embodiments of the present embodiment, TFT elements are used as the amplification element 2, the reading element 3, and the reset element 4.

The sensor element 1 is an element that detects incidence of radiation irradiated to an object on the active pixels 10, and incorporates a capacitive element 1a that accumulates charges corresponding to the radiation dose X. The sensor element 1 may be, for example, a photodiode, and the capacitor element 1a may be, for example, a capacitance between terminals of the sensor element 1. The sensor element 1 has an input terminal to which a bias voltage Vsb from a bias power supply (not shown) is applied, and an output terminal connected to a gate electrode of the amplifying element 2 and a drain electrode of the reset element 4. Further, in a state where the reset element 4 is off, the sensor element 1 applies an electric signal corresponding to the electric charge accumulated in the capacitive element 1a to the gate electrode of the amplification element 2.

In the amplifying element 2, the voltage of the gate electrode (gate voltage) varies according to the electric charge accumulated in the capacitor element 1 a. The amplifying element 2 outputs the change in the gate voltage to the source electrode of the reading element 3 as an amplified current change between the drain and the source. A power supply voltage Vd is applied from a power supply (not shown) of the amplification element 2 to the source electrode of the amplification element 2, and the drain electrode thereof is connected to the source electrode of the reading element 3.

The Read element 3 reads the electric signal amplified by the amplification element 2 as an output current Iout based on the Read signal Read output from the Read element control unit 22, and outputs the output current Iout to the IV amplifier 24.

Specifically, when the Read signal Read input to the gate electrode of the Read element 3 is at a high level, the emitter and the collector of the Read element 3 are turned on, and the Read element 3 outputs the output current Iout. On the other hand, when Read is at a low level, the emitter and the collector are in a cut-off state. That is, the reading element 3 functions as a switching element, and performs reading when turned ON (ON) and interrupts reading when turned OFF (OFF).

The Reset element 4 initializes the active pixel 10 based on a Reset signal Reset _ all output from the Reset element control unit 23. Here, the initialization of the active pixel 10 is to return the potential of the capacitive element 1a to the initial potential Vb so that the voltage between the gate and the source of the amplifying element 2 slightly exceeds a predetermined threshold. For example, if the amplifying element 2 is an N-type TFT element and the prescribed threshold value is 2V, the initial potential Vb is set to about Vb of 3V.

The reason why the active pixel 10 is initialized is that if the charge accumulation is excessive and the potential of the capacitive element 1a becomes excessive, the output current Iout output by the amplifying element 2 is saturated, and further, the output voltage Vout is saturated. Therefore, by returning the potential of the capacitive element 1a to the initial potential Vb before the potential becomes excessively large, the amplification element 2 can be operated at an appropriate signal amplification factor.

Specifically, when the Reset signal Reset _ all input to the gate electrode of the Reset element 4 is at a high level, the emitter and the collector of the Reset element 4 are turned on and the capacitive element 1a is connected to the initial potential Vb. On the other hand, when the Reset signal Reset _ all is at a low level, the emitter and the collector are in a cut-off state. That is, the reset element 4 functions as a switching element, and performs initialization when turned on, and interrupts initialization (i.e., charge accumulation in the capacitive element 1a) when turned off.

< image capturing operation of radiographic imaging apparatus >

Next, an image capturing operation of the radiation image capturing apparatus 100 will be described with reference to fig. 6 and 7. Fig. 6 is a diagram showing a timing chart of an image capturing operation of the radiation image capturing apparatus 100. Fig. 7 is a graph showing a relationship between the dose X of radiation incident on the active pixel 10 and the output voltage Vout.

As shown in fig. 6, the image capturing operation of the radiation image capturing apparatus 100 is composed of two stages (phase) of an initialization period and an image data generation period. The image data generation period is constituted by three stages of a first reading period, a second reading period, and an additional period for signal accumulation.

The additional period for signal accumulation is an additional period added as necessary to secure a signal accumulation time for acquiring a necessary signal intensity, and the time length may be zero, that is, the additional period may not be set. The length of the additional period for signal accumulation is defined as a subframe. The additional period for signal accumulation also functions as a redundant period for ensuring the consistency of the frame period.

Further, the elapsed time of the first reading period and the respective time lengths of the second reading period are regarded as one sub-frame. Here, one sub-frame specifically refers to a time required to read the output voltages Vout _1 to Vout _4 from the respective columns of the active pixels 10. The time length of the first reading period is defined as a first sub-frame, and the time length of the second reading period is defined as a second sub-frame.

In the following description, after the active pixel 10 is initialized first, the output current of the active pixel 10 in the ith row and the jth column, which is Read in the high level period of the nth time of the Read signal Read _ i in the uninitialized state, is Iout (i, j, n), and the output voltage is Vout (i, j, n). The radiation dose of the radiation incident on the active pixels 10 in the ith row and the jth column before the nth reading is X (i, j, n).

(initialization period)

First, before the image data generation period starts, the Reset element control section 23 outputs a first high-level Reset signal Reset _ all from the output terminal to which the gate electrodes of all the Reset elements 4 are connected, turns on all the Reset elements 4, and initializes all the active pixels 10. Here, the initialization time (i.e., the time length of the initialization period) required for the initialization of the active pixel 10 is determined based on the capacitance of the capacitive element 1a, the resistance value of the line to which the initial potential Vb is applied, and the impedance of the voltage source of the initial potential Vb.

By performing such control, data of a two-dimensional image of 4 × 4 resolution can be smoothly and continuously generated over a plurality of frames without initializing the active pixels 10 immediately after the start of the image data generation period.

In the present embodiment, every time 3 image data generation periods required to generate data of 3 two-dimensional images from a total of 16 active pixels 10 arranged in a 4 × 4 matrix are passed, all the active pixels 10 are initialized. That is, in the present embodiment, the initialization period for initializing each of all the active pixels is a total time length of 4 frames (a time length of a plurality of frames, see fig. 6) and 3 subframes (see fig. 6). Then, the reset element control section 23 collectively initializes all the active pixels 10 at a point in time when 4 frames have elapsed.

However, the initialization period of the active pixel 10 is not limited to the above. That is, the initialization is performed to prevent saturation of the output voltage Vout, which is caused by the capacitor element 1a being in a saturated state (a state in which charge cannot be accumulated). Alternatively, the saturation is caused by saturation of the output current Iout of the amplification element 2 due to an excessive voltage applied to the gate electrode of the amplification element 2. Therefore, the initialization period can be determined by calculating in advance the time required for the amount of charge accumulated in the capacitive element 1a that is temporarily initialized to reach a threshold value (for example, an amount of charge slightly smaller than the amount of charge in the state of saturation of the capacitive element 1 a). For example, assuming that the maximum input of the radiation dose X of radiation incident on the active pixels 10 is continued, the initialization period (number of frames) can be determined after determining in advance how long it takes to reach the threshold value.

Note that, unlike the present embodiment, it is not necessary to initialize all the active pixels 10 at once for each initialization period, and, for example, one or more rows of active pixels 10 may be initialized sequentially for each frame (see embodiment two). In other words, the reset element control section 23 may initialize each of all the active pixels 10 within the initialization period so that all the active pixels 10 are initialized at the end of the initialization period.

In addition, in order to achieve the object of increasing the frame rate of the present invention, the initialization period must be defined as a time length of a plurality of frames, or a total time length of a plurality of frames and a plurality of subframes.

(image data creation period)

After the initialization of all the active pixels 10 is completed, the operation of generating data of a two-dimensional image of 4 × 4 resolution is started. That is, the first image data generation period is started. Specifically, the Reset element control unit 23 outputs a first low-level Reset signal Reset _ all from the output terminal, and turns off all the Reset elements 4. At the same time, the reading element control section 22 sequentially outputs a first high-level reading signal Read _1, a first reading signal Read _2, a first reading signal Read _3, and a first reading signal Read _4 from the respective output terminals to which the gate electrodes of the reading elements 3 in each row of the active pixels 10 are connected.

Then, the output current Iout (i, 1, 1), the output current Iout (i, 2, 1), the output current Iout (i, 3, 1), and the output current Iout (i, 4, 1) are sequentially read by the respective reading elements 3 for each column of the active pixels 10 (1 column is configured by 4 active pixels 10).

The read 4 output currents Iout are converted into output voltages Vout (i, 1, 1), Vout (i, 2, 1), Vout (i, 3, 1), and Vout (i, 4, 1) by the IV amplifier 24, respectively, and output to the image data generation unit 25. When all of the 4 output voltages Vout (first outputs) are input to the image data generating unit 25, the first reading period for the first time ends.

After the first read period for the first time ends, the second read period for the first time starts. In the second reading period, the reset element control unit 23 and the reading element control unit 22 also perform the same signal output control as in the first reading period. Then, 4 output voltages Vout (second outputs) of the output voltage Vout (i, 1, 2), the output voltage Vout (i, 2, 2), the output voltage Vout (i, 3, 2), and the output voltage Vout (i, 4, 2) are sequentially output to the image data generating unit 25.

Next, the image data generating section 25 generates one piece of two-dimensional image data based on the output voltage Vout read in the first reading period of the first time and the output voltage Vout read in the second reading period of the first time.

Specifically, the image data generation unit 25 assumes that the amount of change Δ X in the radiation dose X of the radiation incident on the active pixels 10 and the amount of change Δ V in the output voltage Vout corresponding to the radiation dose X have a proportional relationship as shown in fig. 7 (Δ V ═ α · Δ X, a proportional constant; α), and calculates the amount of change Δ X. The image data generation unit 25 generates data of a two-dimensional image proportional to the calculated change amount Δ X for each active pixel 10, and acquires data of one two-dimensional image of 4 × 4 resolution.

That is, when the output voltage of the active pixel 10 in the ith row and the jth column Read in the high level period of the first time of the Read signal Read _ i is Vout (i, j, 1) and the output voltage Read in the high level period of the second time of the Read signal Read _ i is Vout (i, j, 2), a relationship of Vout (i, j, 2) -Vout (i, j, 1) ═ α { X (i, j, 2) -X (i, j, 1) } is established. Therefore, by calculating Vout (i, j, 2) -Vout (i, j, 1), the amount of change Δ X in the radiation dose X of the radiation incident on the active pixel 10 from the first reading period to the second reading period is calculated.

The Read time of the output voltage Vout of each active pixel 10, that is, the high-level period of the Read signal Read, is sufficiently shorter than the incident time of radiation incident on the active pixel 10. Therefore, in each of the following embodiments of the present embodiment, in a period (high-level period of the Read signal Read _ i) in which the output voltage Vout is Read from the active pixel 10 in the ith row and jth column in the first Read period and the second Read period, the radiation dose X of the incident radiation and the output voltage Vout corresponding to the radiation dose X are regarded as being constant.

As described above, the image data generating unit 25 acquires data of one 4 × 4-resolution two-dimensional image, and ends the first image data generating period together with the second reading period.

In the second and subsequent image data generation periods, the image data generation unit 25 also acquires data of two-dimensional images of 4 × 4 resolution by the same method as described above.

That is, when the output voltage of the active pixel 10 in the ith row and jth column Read in the nth high-level period of the Read signal Read _ i is Vout (i, j, n) and the output voltage Read in the (n +1) th high-level period of the Read signal Read _ i is Vout (i, j, n +1), a relationship of Vout (i, j, n +1) -Vout (i, j, n) ═ α { X (i, j, n +1) -X (i, j, n) } is established. Therefore, the variation Δ X is calculated by calculating Vout (i, j, n +1) -Vout (i, j, n).

In other words, the image data generation unit 25 obtains the difference between the output voltage (second amplified output) Vout (i, j, n +1) and the output voltage (first amplified output) Vout (i, j, n) read by the reading element control unit 22, thereby generating the change amount Δ X (read output corresponding to the radiation dose of the radiation). The image data generation unit 25 generates data of a two-dimensional image proportional to the change amount Δ X for each active pixel 10.

In addition, the second reading period in the first image data generation period is the first reading period in the second image data generation period. In addition, the second reading period in the second image data generation period is the first reading period in the third image data generation period.

< image capturing processing by radiation image capturing apparatus >

Next, an image capturing process of the radiation image capturing apparatus will be described with reference to fig. 8. Fig. 8 is a flowchart showing this process. In the following description, a specific active pixel 10 is taken as an example. The same description is of course applied to the other active pixels 10.

As shown in fig. 8, first, the Reset element control section 23 outputs a high-level Reset signal Reset _ all before image capturing is started, and initializes the active pixels 10 (all other active pixels 10 are initialized) (step 100: an image capturing preparation step, hereinafter abbreviated as S100).

When radiation irradiated to the subject enters the active pixels 10 after the image capturing is started, the sensor element 1 accumulates charges corresponding to the radiation dose X of the incident radiation in the capacitor element 1a (S101; charge accumulation step).

Then, the reset device control section 23 determines whether or not the 3 image data generation periods have elapsed (S102; initialization execution determination step). If it is determined as YES in S102 (YES, hereinafter abbreviated as Y), the reset element control unit 23 initializes the active pixels 10 (all other active pixels 10 are initialized), and proceeds to the process of S101 again (S103; initialization execution step).

On the other hand, if it is determined in S102 as NO (NO, hereinafter abbreviated as N), the reset device control unit 23 transmits the determination result to the reading device control unit 22. The reading element control section 22 that has received the determination result outputs the high-level reading signal Read (S104; reading signal output step).

Next, the active pixel 10 to which the high-level Read signal Read is input turns on the amplifying element 2 and the reading element 3. Then, the output voltage Vout corresponding to the electric charge accumulated in the capacitor element 1a is read from the active pixel 10 by the IV amplifier (S105; output reading step). The read output voltage Vout is output to the image data generation unit 25.

Subsequently, the image data generation unit 25 determines whether or not the input output voltage Vout has been read in the second reading period (S106; calculation execution determination step). If it is determined at S106 that Y is present, the image data generation unit 25 calculates the amount of change Δ X in the radiation dose X of the radiation incident on the active pixels 10 based on the difference between the output voltage Vout input during the second reading period and the output voltage Vout input during the first reading period stored in the memory (S107; calculation execution step). The memory may be incorporated in the image data generation unit 25 or may be provided externally.

On the other hand, when it is determined at S106 that N is present, the image data generation unit 25 stores the input output voltage Vout in the memory without performing the calculation of the change amount Δ X, and proceeds to the process at S101 again.

After the amount of change Δ X is calculated, the radiographic imaging device 100 determines whether there is an imaging end operation by the user (S108; imaging end determination step). This determination may be performed by an imaging end determination unit (not shown) provided in the radiographic imaging device 100, for example. The operation may be performed by an operation input unit and a power switch unit (both not shown) provided in the same radiographic imaging device 100.

If it is determined at S108 that Y is present, the radiographic imaging device 100 ends the image capturing process. On the other hand, if it is determined at S108 that N is present, the process proceeds to S101 again.

In this way, the radiographic imaging device 100 does not initialize all the active pixels 10 in the first reading period and the second reading period, that is, in each of the first frame and the second frame which are consecutive, and reads the output voltage Vout corresponding to the first frame and the output voltage Vout corresponding to the second frame from all the active pixels 10. Further, the operation of reading the output voltage Vout between the consecutive 2 frames is repeated in the initialization period constituted by a plurality of frames. Therefore, it is possible to suppress power consumption while increasing the frame rate, as compared with the case where all the active pixels 10 of each frame are initialized.

[ second embodiment ]

Another embodiment of the present invention is described below with reference to fig. 9 and 10. For convenience of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiments, and explanations thereof are omitted.

As shown in fig. 9, the radiation image capturing apparatus 200 according to the present embodiment is different from the radiation image capturing apparatus 100 according to the first embodiment in that the output terminal of the Reset device control section 23 is connected to the gate electrode of the reading device 3 of each row of the active pixels 10, and outputs Reset signals Reset _1 to Reset _ 4. The radiographic imaging device 200 is also different from the radiographic imaging device 100 in that only 4 active pixels 10 constituting 1 line are initialized between frames.

< image capturing operation of radiographic imaging apparatus >

Hereinafter, an image capturing operation of the radiographic imaging device 200 will be described with reference to fig. 10. Fig. 10 is a diagram showing a timing chart of an image capturing operation of the radiation image capturing apparatus 200.

As shown in fig. 10, the image capturing operation of the radiographic imaging device 200 is constituted by one stage (phase) of the image data generation period. The image data generation period is constituted by two stages of a first initialization/read period and a second initialization/read period, and the time length of both periods is 1 frame. Further, the first initialization/read period is a first frame, and the second initialization/read period is a second frame. In the present embodiment, although an additional period for signal accumulation between frames is not set, it goes without saying that the additional period may be set.

First, the Read element control unit 22 sequentially outputs a first high-level Read signal Read _1, a first Read signal Read _2, a first Read signal Read _3, and a first Read signal Read _4 from the respective output terminals. At this time, the reading element control section 22 controls signal output so that only the reading signal Read _1 is temporarily interrupted during the high level period.

Next, at the time point when the first half of the high period of the Read signal Read _1 for the first time is interrupted, the Reset element control section 23 outputs the Reset signal Reset _1 for the first time at the high level to start the initialization of each active pixel 10 in the first row. That is, the falling edge of the high period of the first half of the first Read signal Read _1 is synchronized with the rising edge of the first high Reset signal Reset _ 1.

Next, the reading element control section 22 controls the signal output so that the high level period of the second half of the first Read signal Read _1 is restarted at the time point when the high level period of the first Reset signal Reset _1 is ended. That is, the falling edge of the first high Reset signal Reset _1 is synchronized with the rising edge of the high period in the second half of the first Read signal Read _ 1.

In the present embodiment, the active pixel 10 is initialized during the interruption period of the reading of the output voltage Vout. However, the method is not necessarily limited to such a method of reading and initializing, and for example, the initialization of the active pixels 10 may be performed simultaneously during a period in which the high level period of the first Reset signal Reset _1 is continued without interruption.

Here, for each active pixel 10 of the first row being initialized, the output voltage read immediately before the initialization is set to Vout5(1, j, 1), and the output voltage read immediately after the initialization is set to Vout1(1, j, 1). The read output voltages of the active pixels 10 in the other rows are Vout4(2, j, 1), Vout3(3, j, 1), and Vout2(4, j, 1).

The read output voltages Vout are output to the image data generation unit 25. When all of the output voltages Vout are input to the image data generation unit 25, the first initialization/reading period for the first time ends.

After the first initialization/read period for the first time is finished, a second initialization/read period for the first time is started. Specifically, the reading element control section 22 outputs each reading signal Read for the second time so that only the reading signal Read _2 is temporarily interrupted during the high level period.

The Reset element control section 23 outputs the second high-level Reset signal Reset _2 to initialize each active pixel 10 in the second row after the high-level period of the second Read signal Read _2 is interrupted.

Here, for each active pixel 10 of the second row, the output voltage read immediately before the initialization is set to Vout5(2, j, 2), and the output voltage read immediately after the initialization is set to Vout1(2, j, 2). In addition, the read output voltages of the active pixels 10 in the other rows are Vout2(1, j, 2), Vout 4(3, j, 2), and Vout 3(4, j, 2), respectively. The read output voltages Vout are output to the image data generation unit 25.

Next, the image data generating section 25 generates data of one two-dimensional image based on the output voltage Vout read in the first initialization/reading period of the first time and the output voltage Vout read in the second initialization/reading period of the first time.

That is, for each active pixel 10 in the first row, when the output voltage of the active pixel 10 in the j-th column in the 1 st row Read in the high level period in the second half of the first time of the Read signal Read _1 is Vout1(1, j, 1) and the output voltage Read in the high level period in the second time of the Read signal Read _1 is Vout2(1, j, 2), the relationship between Vout2(1, j, 2) -Vout1(1, j, 1) ═ α { X (1, j, 2) -X (1, j, 1) } holds. Therefore, by calculating Vout2(1, j, 2) -Vout1(1, j, 1) for each active pixel 10 in the first row, the image data generation unit 25 calculates the amount of change Δ X in the radiation dose X of the radiation incident on each active pixel 10 from the first initialization/read period to the second initialization/read period.

As described above, the image data generating unit 25 acquires data of one 4 × 4-resolution two-dimensional image, and ends the first image data generating period together with the first second initialization/reading period.

That is, when the active pixel 10 in the i-th row is initialized in the nth initialization/Read period, the output voltage of the active pixel 10 in the j-th column in the i-th row Read in the high level period in the second half of the n-th time of the Read signal Read _ i is Vout1(i, j, n), and the output voltage Read in the high level period in the n + 1-th time of the Read signal Read _ i is Vout2(i, j, n +1), the relationship Vout2(i, j, n +1) -Vout 1(i, j, n) - α { X (i, j, n +1) -X (i, j, n) } is established. Therefore, by calculating Vout2(i, j, n +1) -Vout 1(i, j, n), the amount of change Δ X in the active pixels 10 of the i row is calculated.

In addition, the second initialization/read period in the image data generation period of the nth time becomes the first initialization/read period in the image data generation period of the (n +1) th time.

In this way, in the radiographic imaging device 200, the reset element control unit 23 initializes the active pixels 10 in different rows for each frame. Since at least any one of the active pixels 10 is initialized in each frame, it is not necessary to set a period for suspending the generation of data of the two-dimensional image so as to uniformly initialize all the active pixels 10. Therefore, data of a plurality of two-dimensional images can be continuously generated without interruption, and the frame period can be secured without providing a redundant period, which is an additional period for accumulating signals as in the first embodiment.

In addition, since the actual number (i × j) of active pixels 10 included in the radiographic imaging device according to the present invention is much larger than 4 × 4, actually, a plurality of rows (for example, several tens of rows) of active pixels 10 are initialized in one frame among a plurality of frames constituting the initialization period.

[ third embodiment ]

Another embodiment of the present invention is described below with reference to fig. 11 and 12. For convenience of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiments, and explanations thereof are omitted.

The radiographic imaging device 300 according to the present embodiment is different from the radiographic imaging devices 100 and 200 according to the first and second embodiments in that the image data generation unit 25 represents the relationship between the dose X of radiation incident on the active pixels 10 and the output voltage Vout read from the active pixels 10 using an approximate function, and calculates the amount of change Δ X in the dose X of radiation.

The configuration of the main portion of the radiographic imaging device 300 is the same as that of the main portion of the radiographic imaging device 100 according to the first embodiment. The control of signal output by the reading element control section 22 and the reset element control section 23 provided in the radiographic imaging device 300 is also the same as that of the radiographic imaging device 100 (see fig. 5). However, the configuration of the main parts of the radiographic imaging device 300 and the like may be the same as, for example, the radiographic imaging device 200 according to the second embodiment.

< calculation of amount of change in radiation dose of radiation by image data generating section >

The following describes calculation of the amount of change Δ X in the radiation dose X of the radiation by the image data generation unit 25, with reference to fig. 11 and 12. Fig. 11 is a graph showing a relationship between the dose X of radiation incident on the active pixels 10 included in the radiation image capturing apparatus 300 and the output voltage Vout read from the active pixels 10. Fig. 12 is a graph showing a relationship between the radioactive dose X and the output voltage Vou as an approximation function.

In the case of actually testing the radiation dose X of radiation incident on the active pixels 10 and the output voltage Vout read from the active pixels 10, as shown in fig. 11, nonlinearity occurs. This phenomenon is caused by the fact that the relationship between the gate voltage and the drain current of the amplifying element 2 is not linear, and the characteristics of the sensor element 1 have an inter-terminal voltage dependency.

Further, when the imaging operation is repeated without initializing the active pixel 10, the amount of charge accumulated in the capacitive element 1a increases, and therefore the width of change in the gate voltage of the amplification element 2 increases accordingly, and the nonlinearity becomes more significant.

Therefore, in order to more accurately calculate the variation Δ X of the radiation dose X of radiation incident from the output voltage Vout, it is necessary to derive an approximation function by correcting the relationship of the output voltage Vout and the radiation dose X to be close to the actually measured nonlinearity, and calculate the variation Δ X by using the approximation function. Hereinafter, a method of deriving the approximation function will be described.

(derivation method of approximation function)

First, a fixed dose of radiation is uniformly and continuously irradiated onto the surface of the imaging panel 20 on which the active pixels 10 are arranged. And, for a particular active pixel 10, the output voltage immediately after initialization is V0, after which V1, V2, V3, V4,.. the VN and the output voltage Vout are read at every fixed frame (either every frame or every few frames). Based on the read data of the output voltage Vout, as shown in fig. 11, the relationship between the radiation dose X and the output voltage Vout corresponding to the radiation dose X is graphed.

Here, X1, X2, X3, X4.., XN denotes a radiation dose X of radiation incident on the above-described specific active pixel 10. However, since the output voltage Vout is read every fixed frame in which a fixed dose of radiation is irradiated, it is not necessary to represent it by its absolute value, but it may be arbitrarily represented so as to satisfy X1 ═ X2-X1 ═ X3-X2 ═ X4-X3 · ═ XN-X (N-1).

Next, regarding the relationship between the radiation dose X of radiation and the output voltage Vout corresponding to the radiation dose X shown in the graph of fig. 11, an approximate function X ═ f (Vout) shown in the graph of fig. 12 is derived by regarding X as a function of Vout.

The derived approximation function X ═ f (vout) is associated with a formula for calculating the amount of change Δ X in the radiation dose X of the radiation incident on all the active pixels 10, and is stored in a memory (not shown) incorporated in the image data generating unit 25. The memory may be provided outside the image data generation unit 25.

The approximation function X ═ f (vout) may be derived individually for each active pixel 10. In other words, the image data generator 25 may use the approximation function X ═ f (vout) corresponding to each of all the active pixels 10. By using the approximation function X ═ f (vout) for each active pixel 10, the variation Δ X in the radiation dose X of radiation can be calculated more accurately.

Further, a graph is created that averages the relationship between the radiation dose X of the radiation of each active pixel 10 and the output voltage Vout corresponding to the radiation dose X, and an approximation function X ═ f (Vout) derived based on the graph is associated with all the active pixels 10.

Further, the approximation function X ═ f (vout) may also be derived by the user through experiments or the like. Alternatively, the approximation function deriving section may be provided inside or outside the image data generating section 25 so as to be automatically derived by incidence of radiation on the active pixels 10.

(calculation of amount of change in radiation dose of radiation using approximation function)

The image data generation unit 25 calculates the amount of change Δ X in the radiation dose X of the radiation incident on the active pixel 10 using the approximation function X ═ f (vout) derived by the method described above.

That is, when the output voltage of the active pixel 10 in the ith row and the jth column Read in the nth high-level period of the Read signal Read _ i is Vout (i, j, n) and the output voltage Read in the (n +1) th high-level period of the Read signal Read _ i is Vout (i, j, n +1), a relationship of f (Vout (i, j, n +1)) -f (Vout (i, j, n)) -X (i, j, n +1) -X (i, j, n) is established. Therefore, the variation Δ X is calculated by calculating f (Vout (i, j, n +1)) -f (Vout (i, j, n)).

In this way, the image data generation unit 25 calculates the amount of change Δ X in the radiation dose X of the radiation incident on the active pixels 10 by using the approximation function X ═ f (vout), and therefore the calculated amount of change Δ X is a value close to the actual measurement value. Therefore, the radiographic imaging device 300 can acquire two-dimensional image data with higher accuracy.

[ software embodiment ]

The control block (particularly, the reading element control section 22 and the reset element control section 23) of the radiographic imaging apparatus 100 may be realized by a logic circuit (hardware) formed of an integrated circuit (IC chip) or the like, or may be realized by software design using a CPU.

In the latter case, the radiographic imaging device 100 includes: a CPU that executes a command as a program designed by software for realizing each function; a ROM (read only Memory) or a storage device (which is referred to as a "storage medium") that can read and store the above-described program and various data in a computer (or CPU); RAM in which the above programs are developed, and the like. The object of the present invention is achieved by reading the program from the storage medium and executing the program by a computer (or CPU). As the storage medium, a "non-transitory tangible medium" such as a magnetic tape, a magnetic disk, a card, a semiconductor memory, a programmable logic circuit, or the like can be used. The program may be supplied to the computer via an arbitrary transmission medium (a communication network, a broadcast wave, or the like) through which the program can be transmitted. In the present invention, the program can be realized in the form of a data signal embodied by electronic transmission and carried on a carrier wave.

[ conclusion ]

A radiographic imaging device (100, 200, 300) according to a first embodiment of the present invention is a radiographic imaging device that acquires a two-dimensional image corresponding to a radiation dose (X) of radiation that has been irradiated onto a subject, and includes: a plurality of pixels (active pixels 10) arranged two-dimensionally; a capacitance element (1a) provided in each of the plurality of pixels, and configured to accumulate, between at least two consecutive frames, electric charges corresponding to the radiation dose per pixel by incidence of the radiation to the plurality of pixels; and a read control unit (read element control unit 22, reset element control unit 23) which reads a first output (output voltage Vout) and a second output (output voltage Vout) corresponding to the accumulated charges from at least one of the plurality of pixels without initializing the at least one pixel for each of a first frame and a second frame constituting the two frames.

According to the above configuration, the read control unit reads the first output and the second output corresponding to the electric charges accumulated in the capacitive element from each of the plurality of pixels arranged two-dimensionally without initializing at least one of the plurality of pixels in each of the first frame and the second frame constituting the two frames. Here, the "one frame" refers to a time required to read data of one two-dimensional image from a plurality of pixels arranged two-dimensionally.

Therefore, for at least one pixel that is not initialized, it is not necessary to consider the time required for the initialization. Therefore, it is possible to reduce the power consumption required for the initialization of one pixel while shortening the total acquisition time of two-dimensional image data, as compared with the case where all of the plurality of pixels of each frame are initialized.

According to the above, it is possible to provide a radiographic imaging device that achieves an improvement in frame rate and a suppression of power consumption.

A radiographic imaging device (100, 200, 300) according to a second embodiment of the present invention is the radiographic imaging device according to the first embodiment, wherein an initialization period in which the initialization is performed for each of the plurality of pixels (active pixels 10) is determined to be a time length of a plurality of frames, and the read control unit (reset element control unit 23) may initialize the plurality of pixels in the initialization period so that the initialization is performed for all of the plurality of pixels at the end of the initialization period.

In a pixel in which the first output and the second output are read without being initialized, the charge amount accumulated in the capacitive element of the pixel increases according to the number of repetitions of the reading. When the amount of charge accumulated over a plurality of frames reaches a predetermined amount, the capacitance element is in a saturated state in which charge cannot be accumulated any more, and the read first output and second output are saturated after the amount reaches the predetermined amount. Therefore, after reaching the prescribed dose, the read first output and second output do not correspond to the radiation dose of the radiation irradiated to the subject.

On the other hand, when each of the plurality of pixels is initialized in the period of one frame and all of the plurality of pixels are initialized within one frame, the time of one frame becomes long.

In this regard, according to the configuration, since all of the plurality of pixels are initialized within the time of the plurality of frames, the time of one frame can be shortened as compared with the case where all of the plurality of pixels within one frame are initialized. Therefore, the radiographic imaging device can read the first output and the second output corresponding to the radiation dose of radiation while shortening the time for one frame.

A radiographic imaging device (100, 200) according to a third embodiment of the present invention is the radiographic imaging device according to the first or second embodiment, wherein the plurality of pixels (active pixels 10) further include an amplifying element (2) that amplifies the first output or the second output, and the read control unit (read element control unit 22) further includes an output generation unit (image data generation unit 25) that reads, from each of the plurality of pixels, a second amplified output (output voltage Vout) that amplifies the second output and a first amplified output (output voltage Vout) that amplifies the first output, and determines a difference between the first amplified output and the second amplified output read by the read control unit, thereby generating a read output (change amount Δ X) corresponding to a radiation dose (X) of the radiation.

According to the above configuration, the plurality of pixels further include an amplifying element that amplifies the first output or the second output, and the read control unit reads the second amplified output that amplifies the second output and the first amplified output that amplifies the first output from each of the plurality of pixels. Therefore, even when noise or the like occurs in the read control unit, the radiographic imaging device can more reliably read the output from each of the plurality of pixels as the first amplified output and the second amplified output.

Further, according to the above configuration, the radiographic imaging apparatus further includes an output generation unit that obtains a difference between the first amplified output and the second amplified output, and generates a read output corresponding to a radiation dose of radiation irradiated to the subject. Therefore, even when the pixels to be read are not initialized in the two frames corresponding to the reading of the first and second amplified outputs, the radiographic imaging device can obtain the radiation dose of the radiation incident on the pixels from the reading time point of the first amplified output to the reading time point of the second amplified output using the read outputs at a value close to the actual measurement.

Further, according to the above configuration, the image data of each frame is obtained by subtracting the output read immediately after the initialization from the read output after the charge accumulation period. Since noise accumulated in the pixels at the time of initialization is eliminated by such a reading action using double sampling, the radiographic imaging device can acquire image data with less noise.

A radiographic imaging device (300) according to a fourth embodiment of the present invention is the radiographic imaging device according to any one of the first to third embodiments, the output generation section (image data generation section 25) uses a radiation dose (X) indicating radiation continuously irradiated to the specific pixel (active pixel 10) initialized, and an approximate function (X ═ f (Vout)) of a relationship between the output (output voltage Vout) and the electric charge accumulated in the capacitor element (1a) according to the radiation dose, the read output (variation amount Δ X) may also be generated by finding a difference between a second correction output (f (Vout)) obtained by substituting the second amplified output (output voltage Vout) into the approximation function and a first correction output (f (Vout)) obtained by substituting the first amplified output (output voltage Vout) into the approximation function.

According to the above configuration, the output generation unit generates the read output by obtaining a difference between the second correction output obtained by substituting the second amplified output into the approximation function and the first correction output obtained by substituting the first amplified output into the approximation function, using the approximation function indicating a relationship between the dose of radiation continuously irradiated to the initialized specific pixel and the output corresponding to the electric charge accumulated in the capacitance element based on the dose of radiation.

Here, since the approximation function represents the relationship between the radiation dose of radiation incident on the pixel and the output from the pixel corresponding to the radiation dose in a form close to the actual measurement, the first correction output and the second correction output are values closer to the actual test value of the radiation dose of radiation irradiated to the subject. Therefore, the output generation unit can generate the read output closer to the actual test value than in the case where the difference between the second amplified output and the first amplified output is found.

A radiographic imaging device (300) according to a fifth embodiment of the present invention is the radiographic imaging device according to the fourth embodiment, and the output generation unit (image data generation unit 25) may use the approximation function (X ═ f (vout)) corresponding to each of the plurality of pixels (active pixels 10).

The relationship between the dose of radiation incident on a pixel and the output from the pixel corresponding to the dose of radiation differs among a plurality of pixels due to differences in characteristics of elements provided in the pixels, differences in arrangement positions of the pixels on the imaging panel, and the like.

In this regard, according to the configuration, the output generation section generates the read output corresponding to each of the plurality of pixels by using the approximation function corresponding to each of the plurality of pixels. Therefore, for example, the output generation unit can generate the read outputs closer to the actual test values of the corresponding pixels than in the case where the approximation function corresponding to a specific pixel is used as the approximation function of another pixel.

A radiographic imaging method according to a sixth aspect of the present invention is a radiographic imaging method for acquiring a two-dimensional image corresponding to a radiation dose (X) of radiation with which a subject is irradiated, the radiographic imaging method including: a charge accumulation step (S101) for accumulating, between at least two consecutive frames, charges corresponding to the radiation dose per pixel by causing the radiation to enter a plurality of pixels (active pixels 10) arranged in the two-dimensional manner; and an output reading step (S105) of reading, for at least one pixel of the plurality of pixels, a first output (output voltage Vout) and a second output (output voltage Vout) corresponding to the accumulated charges from the pixel without initializing the at least one pixel in each of a first frame and a second frame constituting the two frames.

According to the above configuration, it is possible to provide a radiographic imaging method that achieves an improvement in frame rate and a suppression of power consumption.

The radiographic imaging device (100, 200, 300) according to each aspect of the present invention may be realized by a computer, and in this case, a control program for realizing the radiographic imaging device by a computer by operating a computer as each unit (only software elements) provided in the radiographic imaging device and a computer-readable storage medium storing the program also fall within the scope of the present invention.

According to the above configuration, it is possible to provide a program and a storage medium that enable radiographic imaging with an improved frame rate and with suppressed power consumption.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention. Further, by combining the technical means disclosed in the respective embodiments, new technical features can be formed.

Description of the symbols

1a capacitive element

2 amplifying element

10 active pixel (pixel)

22 read element control unit (read control unit)

23 resetting element control part (resetting control part)

25 image data generating part (output generating part)

100. 200, 300 radiation image pick-up device

Claims

1. A radiographic imaging device that acquires a two-dimensional image corresponding to a radiation dose of radiation with which an object is irradiated, the radiographic imaging device comprising:

a plurality of pixels arranged two-dimensionally;

a capacitance element provided in each of the plurality of pixels, and configured to accumulate charges corresponding to the radiation dose per pixel between at least two consecutive frames by incidence of the radiation to the plurality of pixels;

a read control unit that reads, from at least one pixel of the plurality of pixels, a first output read in the first frame and a second output read in the second frame corresponding to the accumulated electric charges, without initializing the at least one pixel in each of the first frame and the second frame constituting the two frames,

an initialization period for performing the initialization for each of the plurality of pixels is determined as a time length of a plurality of frames,

the read control unit initializes the plurality of pixels in the initialization period so that all of the plurality of pixels are initialized at the end of the initialization period, while performing the initialization on a certain number of different pixels in each of the plurality of frames.

2. A radiographic imaging device according to claim 1,

the plurality of pixels further include an amplifying element for amplifying the first output or the second output,

the read control unit further includes an output generation unit that reads, from each of the plurality of pixels, a second amplified output obtained by amplifying the second output and a first amplified output obtained by amplifying the first output,

the reading control unit generates a reading output corresponding to the radiation dose by obtaining a difference between the first and second amplification outputs read by the reading control unit.

3. A radiographic imaging device according to claim 2,

the output generation unit generates the read output by obtaining a difference between a second correction output obtained by substituting the second amplified output into the approximation function and a first correction output obtained by substituting the first amplified output into the approximation function, using an approximation function representing a relationship between a radiation dose of radiation continuously irradiated to the initialized specific pixel and an output corresponding to electric charges accumulated in the capacitive element according to the radiation dose.

4. A radiographic imaging device according to claim 3,

the output generation section uses the approximation function corresponding to each of the plurality of pixels.